Faith is the means that this kind and severe God has established by which his grace is brought to bear upon the condition of the estranged. We are saved by grace through faith. Humans who express such faith get saved, those who won't, don't. A statement like that is likely to bend some Calvinists into a pretzel, probably a salty one, but it reflects the Bible on the subject, what can be wrong with that? Faith has always been, and always will be the issue with human beings in regard to their relationship with God.
Faith is not a static thing, however, it has a shelf life, a relatively short one, it seems to me. To envision faith as if it was like a switch--once turned on it stays on, without thought-- is a mistake in my view. Faith is a dynamic conviction, a motivating understading that has power while its active, but diminishes when its not. Faith has ebb and flow, it does not exist in the static universe, but only in the realm of action. Try to put it on a shelf, like oil in a lamp, unused, untended, and inactive, it evaporates and won't be there to bear light when needed. It not only has to be engaged to function, it has to function to exist.
Can we learn a lesson from the traveling Israelites, whose sustenance, like ours, was dependent upon God's grace? Faith is like manna, it's good for today, but does not project to tomorrow. Even the pot collected to serve as a communal memorial has long since turned to dust and blown away. Faith is a working thing, and a present thing. Manna could never serve as a knick-knack, neither can faith.